Continuing from the previous post, we¹re going to idle the 1st section of
the 6922 tube a bit higher.

1. If we select a plate resistor of 16K, this gives us a new end point on
our load line of about 14.5 mA. Using the ³manual method² (i.e. ruler and
load line), if we bias the grid at *2.5V that corresponds to a plate voltage
of about 113V. That gives a voltage drop of 120, which sets the idling
current of the tube at 7.5 mA.

2. If we plug the numbers into TubeCad, the results change to:

Rk = 340 ohms

Gain = 12.83 (increase of 1.45 or about 13%)
Z input = 307K (slight decrease)
F -3dB low = 17.4 hz; F -3dB high = 877 khz
Z out 5.66kK (assuming an RL of 22K which may be wrong)
Vo max = -51/+69.5v (significant increase in swing)
PSRR = -9.02 dB

At this point we are operating in a more linear region of the tube.

3. TubeCad allows us to predict the effect of adding a cathode bypass cap,
say about 100 MFD. The outcome is pretty interesting:

Gain = 24.93 (doubled!)
Z input = 186K (~40% decrease)
F -3dB low = 19.9 hz; F -3dB high = 452 khz
Z out 2.27K (assuming an RL of 22K which may be wrong)
Vo max = -64/+69.5v (significant increase in swing)
PSRR = -17 dB

4. Looks pretty good except I don¹t like a *3dB point of 20 Hz. Good for
motorboating maybe but bad for Bach.

5. If we sub a 22K resistor for the 10K grid stopper, -3dB point drops to
15 Hz; the high point drops to 201 Khz.

Any suggestions?

Jon Yaeger wrote:

Continuing from the previous post, we¹re going to idle the 1st section of
the 6922 tube a bit higher.

1. If we select a plate resistor of 16K, this gives us a new end point on
our load line of about 14.5 mA. Using the ³manual method² (i.e. ruler and
load line), if we bias the grid at *2.5V that corresponds to a plate voltage
of about 113V. That gives a voltage drop of 120, which sets the idling
current of the tube at 7.5 mA.

2. If we plug the numbers into TubeCad, the results change to:

Rk = 340 ohms

Gain = 12.83 (increase of 1.45 or about 13%)
Z input = 307K (slight decrease)
F -3dB low = 17.4 hz; F -3dB high = 877 khz
Z out 5.66kK (assuming an RL of 22K which may be wrong)
Vo max = -51/+69.5v (significant increase in swing)
PSRR = -9.02 dB

At this point we are operating in a more linear region of the tube.

3. TubeCad allows us to predict the effect of adding a cathode bypass cap,
say about 100 MFD. The outcome is pretty interesting:

Gain = 24.93 (doubled!)
Z input = 186K (~40% decrease)
F -3dB low = 19.9 hz; F -3dB high = 452 khz
Z out 2.27K (assuming an RL of 22K which may be wrong)
Vo max = -64/+69.5v (significant increase in swing)
PSRR = -17 dB

4. Looks pretty good except I don¹t like a *3dB point of 20 Hz. Good for
motorboating maybe but bad for Bach.

5. If we sub a 22K resistor for the 10K grid stopper, -3dB point drops to
15 Hz; the high point drops to 201 Khz.

Any suggestions?

Yeah, go back to to answer each and every question I asked in my last post on
the
operation of V1.

Patrick Turner.

in article , Patrick Turner at
wrote on 5/8/05 10:19 AM:



Jon Yaeger wrote:

Continuing from the previous post, we¹re going to idle the 1st section of
the 6922 tube a bit higher.

1. If we select a plate resistor of 16K, this gives us a new end point on
our load line of about 14.5 mA. Using the ³manual method² (i.e. ruler and
load line), if we bias the grid at *2.5V that corresponds to a plate voltage
of about 113V. That gives a voltage drop of 120, which sets the idling
current of the tube at 7.5 mA.

2. If we plug the numbers into TubeCad, the results change to:

Rk = 340 ohms

Gain = 12.83 (increase of 1.45 or about 13%)
Z input = 307K (slight decrease)
F -3dB low = 17.4 hz; F -3dB high = 877 khz
Z out 5.66kK (assuming an RL of 22K which may be wrong)
Vo max = -51/+69.5v (significant increase in swing)
PSRR = -9.02 dB

At this point we are operating in a more linear region of the tube.

3. TubeCad allows us to predict the effect of adding a cathode bypass cap,
say about 100 MFD. The outcome is pretty interesting:

Gain = 24.93 (doubled!)
Z input = 186K (~40% decrease)
F -3dB low = 19.9 hz; F -3dB high = 452 khz
Z out 2.27K (assuming an RL of 22K which may be wrong)
Vo max = -64/+69.5v (significant increase in swing)
PSRR = -17 dB

4. Looks pretty good except I don¹t like a *3dB point of 20 Hz. Good for
motorboating maybe but bad for Bach.

5. If we sub a 22K resistor for the 10K grid stopper, -3dB point drops to
15 Hz; the high point drops to 201 Khz.

Any suggestions?

Yeah, go back to to answer each and every question I asked in my last post on
the
operation of V1.

Patrick Turner.


Thanks, Patrick! Hope you're not in a hurry for those answers . . .